It actually does matter. A lot. Because the sons of Abraham represent different covenants.
For background, God promised Abraham a son. When they didn’t pregnant after more than a year, Sarah suggested he sleep with her servant. He did. And Abraham bore Ishmael through the slave woman.
But this son was not the son of the promise. Nor was he the son of Sarah. The miracle finally did come. And Sarah bore Isaac.
And the two sons have been war even to this very day (literally).
Isaac’s line is the Jewish line. And the muslim’s trace their heritage to Ishmael.
The muslims say that Abraham’s son was Ishmael, even though it is not directly mentioned in the Quran. Let’s read the Quranic verses:
Surah As-Saffat 37:100–112 (Translation)100 He [Abraham] said, “My Lord, grant me [a child] from among the righteous.”
101. So We gave him good tidings of a forbearing boy.
102. And when he reached with him [the age of] exertion, he said, “O my son, indeed I have seen in a dream that I [must] sacrifice you, so see what you think.” He said, “O my father, do as you are commanded. You will find me, if Allah wills, of the steadfast.”
[The Son of Abraham is almost sacrified]
110. Indeed, We thus reward the doers of good.
111. Indeed, he was of Our believing servants.
112. And We gave him good tidings of Isaac, a prophet from among the righteous.
This is where they say it must have been Ishmael, because in ayah (verse) 112 after these events, it mentions Isaac. Ibn Abbas, one of their scholars, believe the son to be Ishmael. While al-Tabari said it could be either Ishmael or Isaac.
What does the Bible say? It is interesting. It says that Isaac was Abraham’s “only son” and that he was the one sacrificed.
🔹 Genesis 22:2 (ESV)
He said, “Take your son, your only son Isaac, whom you love, and go to the land of Moriah, and offer him there as a burnt offering on one of the mountains of which I shall tell you.”
🔹 Genesis 22:12 (ESV)
He said, “Do not lay your hand on the boy or do anything to him, for now I know that you fear God, seeing you have not withheld your son, your only son, from me.”
🔹 Genesis 22:16 (ESV)
“By myself I have sworn, declares the Lord, because you have done this and have not withheld your son, your only son…”
🔹 Hebrews 11:17 (ESV)
By faith Abraham, when he was tested, offered up Isaac, and he who had received the promises was in the act of offering up his only son,
From Genesis to the New Testament, the Bible sees Isaac as the “only son” of Abraham. Yes, Ishmael was born first of the slave woman, but he was not the promised one.
Why is this important?
1) Isaac is the Son of God’s Promise, not Ishmael
“Now you, brothers, like Isaac, are children of promise” (Galatians 4:28).
In Galatians 4 we read how Ishmael is the son of the Law, born of the natural way and not of the promise. But Isaac was born miraculously, and is one of the promise. Isaac is the Son by faith.
Since it is by faith, like Abraham was declared righteous by faith, then it is representative of the promises of righteousness to all who have faith in Christ.
2) Isaac forshadows Christ
As Abraham offered up his son by faith, God offers up his son, Christ.
“By faith Abraham, when he was tested, offered up Isaac, and he who had received the promises was in the act of offering up his only son” (Hebrews 11:17-19).
Isaac was spared. Jesus was not.
3) Isaac foreshadows the gospel
“…‘Through Isaac shall your offspring be named’” (Romans 7:9)
Paul has previously taught that being a descendant of Abraham did not make them true children of God.
6 But it is not as though the word of God has failed. For not all who are descended from Israel belong to Israel,
7 and not all are children of Abraham because they are his offspring, but “Through Isaac shall your offspring be named.”
8 This means that it is not the children of the flesh who are the children of God, but the children of the promise are counted as offspring (Romans 9:6-8).
Paul is teaching that it is through faith that we are children of God, not through the flesh. Flesh alone does not make us a son or daughter. It is through faith. Isaac teaches us that.
For the muslims reading this, remember what the Quran says.
“And We gave to him Isaac and Jacob, and placed in his descendants prophethood and scripture; and We gave him his reward in this world, and indeed, he is in the Hereafter among the righteous” (Quran 29:27).
Even in the Quran it is about Isaac.